1. Field of the Invention
The present invention relates to a simultaneous two-face color printing machine for the printing of cards, particularly cards of plastic.
2. Description of the Prior Art
In the known technology of thermal transfer, the ink is deposited and fixed to the printing medium by means of resistors that form a thermal printing head heating a ribbon coated with inks by means of a modulated electrical current.
There is also the known plastic ribbon technology wherein the primary colors, yellow, magenta and cyan, are deposited sequentially, making it possible, by combinations of different wavelengths called subtractive combinations, to obtain a range of several millions of colors.
The French patent application No. 94 02116 entitled COLOR PRINTING MACHINE, filed on 24 Feb. 1994 by the present applicant, describes a color printing machine wherein the card to be printed on is moved several times successively beneath the same thermal printing head under which the sequentially colored ribbon runs past. In such a machine, after the first color has been printed, the thermal printing head is raised to enable the return of the card to its starting point. The card is then moved again beneath the thermal printing head in the low position for the printing of the second color. The cycle starts again for the printing of the third and final color.
The French patent application no 94 04827 entitled "SYSTEM FOR THE AUTOMATIC TWO-FACE BLACK-AND-WHITE AND COLOR PRINTING OF CARDS BY THE TURNING OVER OF THE CARD" filed by the Applicant on the 15 Apr. 1994, discloses a color printing machine in which the card to be printed is moved by the card-face side several times successively beneath the same thermal printing head under which the sequential color ribbon runs. In such a machine, after the first color has been printed, the thermal printing head is raised to enable the return of the card to its starting point. The card is then moved again beneath the thermal printing head in the low position for the printing of the second color. This cycle starts again for the printing of the third and last color.
The card is then turned over in a turning-over device and presented on the card-back side beneath a thermal printing head, which may be the same as the head used for the card-face side, where it is moved back and forth successively three times as stated here above for the printing of the three primary colors.
However, this system is not entirely satisfactory when large quantities of cards must be printed. Indeed, while a card is going through its printing cycle (namely entry, rotation by .+-.180.degree., exit), a non-negligible period of time elapses during which the printing capacities of the printing head are unused.